1. Field of the Invention
The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and its control method.
2. Description of Related Art
Color image forming apparatuses are conventionally known which perform feed-forward control of image carriers to control the variations in the rotational speed of each image carrier for each color so as to reduce color misregistration and variations (for example, see Japanese Patent Laid-Open No. 09-182488, paragraph Nos. 0022 and 0032, and FIG. 4).
Along with recent demand for high-quality color images without color misregistration and variation, there has also been increased demand for a single image forming apparatus capable of outputting various kinds of images such as monochrome images like documents, full-color images taken with a digital camera or the like, and unicolor images like POP (Point Of Purchase advertising) at a supermarket.
As is proposed in the above-mentioned patent document, a method of calculating correction information for feed-forward control of the rotation of a rotating body such as an image carrier at power-on so that the rotation of the rotating body will be controlled based on the correction information calculated becomes suitable for certain kinds of images because the method reduces rotational variations with respect to the conditions calculated.
However, in the case of color image forming apparatuses, for example of tandem type that combines and outputs different kinds of images such as color images and monochrome images, since the number of toner colors varies with the kind of image, the number of fixing means or the like (load) that directly act on each corresponding image carrier needs to be changed each time an image or combined image is transferred from the image carrier to an intermediate transfer body. Therefore, if it is required to output an image under conditions other than those for which the correction information has been calculated, the above-mentioned type of color image forming apparatuses cannot reduce rotational variations, resulting in a reduction in image quality.